Rotary magnetic actuator



Dem 1957 H. F. RAYFIELD 3,359,517

ROTARY MAGNETIC ACTUATOR Filed Oct. 23, 1965 A'iz N VENTOR. flaw/K 24147510 United States Patent 3,359,517 ROTARY MAGNETIC ACTUATOR Harry F. Rayfield, Arcadia, Califi, assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Oct. 23, 1965, Ser. No. 503,332 2 Claims. (Cl. 335-272) ABSTRACT OF THE DISCLOSURE There is described herein a rotary magnetic actuator for use in high performance digital magnetic tape transports. The actuator provides high torque over a relatively small angular deflection of the output shaft of the actuator. The actuator has the magnetic pole pieces and armature positioned within a concentrical coil surrounded by a frame of magnetic material. The armature and output shaft to which the armature is secured are spaced diametrically apart within the coil to obtain maximum leverage on the output shaft.

1" his invention relates to rotary magnetic actuators and, more particularly, is concerned with an actuator for magnetic tape drive pinch rollers.

Mechanical actuators openated by electromagnetic means are well known. Such actuators are used where it is desired to produce a mechanical movement of limited extent from an electrical control signal. Solenoid type actuators, for example, are incorporated in clutches and brakes, relays, valves and many other similar applications. One use for which the present invention was developed is in the actuation of a pinch roller by which magnetic tape is engaged with a constantly rotating capstan so as to impart movement to the tape through frictional engagement. Such actuators must produce a large force and operate at extremely high speeds for effective use in digital tape recorder systems for example.

The present invention is directed to an actuator which produces extremely high rotational torque with very limited angular motion of the output shaft. The actuator is capable of recycling indefinitely Without wear or deterioration in its mechanical properties. The actuator is completely shielded to eliminate any stray external magnetic fields which might affect the magnetic tape. At the same time, the actuator of the present invention is quiet in operation.

In brief, the present invention includes a hollow cylindrical housing closed at both ends and made of magnetic material such as iron. A coil of wire is concentrically positioned within the cylindrical housing and a pair of pole pieces of magnetic material, secured respectively to the two ends of the housing, project toward each other within the coil. The pole pieces have flat portions lying in a common plane parallel to the axis of the cylindrical housing. A shaft is journalled in the housing and passes through the coil. An elongated piece of magnetic material supported by the shaft forms an armature and has a surface which is moved into engagement with the fiat portions of the pole pieces by rotation of the shaft in one direction. A nonmagnetic stop limits movement of the armature by the shaft in the direction away from the pole faces and spring means normally urges the armature out of engagement with the pole faces and against the stop. The remaining space within the housing including the gap between the armature and the pole faces is filled with a non-viscous liquid.

For a more complete understanding of the invention, reference should be made to the accompanying drawing wherein:

FIGURE 1 is a plan view of the actuator of the present invention; and

FIGURE 2 is a sectional view taken substantially on the line 2-2 of FIGURE 1.

Referring to the drawings in detail, the numeral 10 indicates generally the housing for the actuator assembly. The housing is in the form of a cylindrical shell 12 having an integral end wall 14. The shell fits over the actuator assembly and engages an end wall 16, through which projects the actuator drive shaft 18.

As best shown in FIGURE 2, the shaft 18 extends parallel to the axis of the cylindrical housing 12 but is displaced to one side. The shaft is journalled in a suitable sealed bearing 20 in the end wall 16 and a bearing 22 adjacent the end wall 14.

The shaft 18 is formed with a flat portion 24 to which is secured a clapper member including a laminated iron armature 26 and spacer 28. The clapper assembly is mounted on the shaft 18 by means of a pair of screws 30 which pass through the armature 26 and spacer 28 to engage threaded holes in the shaft 18. Rotation of the shaft 18 permits the clapper to move through the limited space formed by backstop member 32 on one side and a magnetic pole assembly 34. The backstop member is made of nonmagnetic material which is bolted to the end plate 16 by means of screws 36. The backstop member 32 provides a fiat surface 38 against which the armature 26 of the clapper normally rests.

The pole assembly 34 includes three portions all of the same cross-sectional configuration, indicated at 40, 42 and 44. The portions 40 and 42 are of magnetic material and form pole pieces separated by the nonmagnetic spacer portion 44. The pole assembly 34 is provided with a fiat face 46 which is adapted to engage the armature 26 of the clapper assembly. A coil spring 48 positioned in an opening in the spacer portion 44 of the pole assembly 34 presses against the armature 26 of the clapper assembly urging it against the stop member 32 and away from the pole assembly 34.

The stop member 32 and the pole assembly 34 are provided with cylindically curved outer surfaces which, as shown in the cross-section of FIGURE 2, form together with the cylindrical portion 12 of the housing an annular space in which is mounted a coil of wire 50. When the actuator is assembled on the end plate 16 and the cylindrical portion 12 and end portion 14 are secured in position, the interior of the housing is fully enclosed and sealed so as to receive a fluid which completely fills the remaining space within the housing. A fluid having a viscosity even thinner than water is preferred so as to have a minimum damping effect on the high speed movement of the clapper.

In operation, when the coil 50 is energized, a magnetic field is produced having flux lines which follow the low reluctance path indicated by the dash lines in FIGURE 1. Thus the flux passes from one pole portion 40- into the clapper armature 26 and back into the pole portion 42, the flux completing its path through the magnetic material of the outer housing. The flux takes this path because the reluctance of the gap between the pole portions 40 and 42 and the clapper armature 26 is lower than the reluctance path through the nonmagnetic spacer 44. The magnetic field, of course, draws the clapper towards the surface 46 compressing the spring 48. When the current to the coil 50- is interrupted, the spring 48 returns the clapper to its initial position in contact with the surface 38.

The rotary actuator above-described has proved to produce an extremely high torque in a small package. Because the actuating coil is completely enclosed in a housing of magnetic material, no stray external fields are produced. The housing being filled with a liquid provides for quiet operation and reduces the wear between the impacting surfaces to a negligible level.

What is claimed is:

1. An electromagnetic actuator comprising an outer housing of magnetic material having an enclosed substan- I tially cylindrical chamber, a wire coil inside and concentric with the chamber, magnetic pole pieces secured to the housing within the chamber, the pole pieces projecting toward each other within the coil with their inner ends spaced apart to form a non-magnetic gap, an output shaft journalled in the housing and extending through the chamber within the coil, the shaft being positioned away from the axis of the coil and chamber, an elongated armature extending parallel to and diametrically opposite 4 the shaft within the coil, whereby the axis of the coil is positioned between the shaft and the armature, and means including a spacer member supporting the armature from the shaft, the armature bridging substantially the entire length of the chamber in overlapping relation to the pole pieces.

2. Apparatus as defined in claim 1 further including a stop member bridging the chamber within the coil and positioned on the opposite side of the armature from the pole pieces, and a compression spring mounted between pole pieces and engaging the armature for urging the armature away from the pole pieces and against the stop member.

' References Cited UNITED STATES PATENTS 2,767,357 10/1956 Naybor 335--276 X 3,042,842 7/1962 Cox 335248 3,253,195 6/1966 Fischer et al. 335276 BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner. 

1. AN ELECTROMAGNETIC ACTUATOR COMPRISING AN OUTER HOUSING OF MAGNETIC MATERIAL HAVING AN ENCLOSED SUBSTANTIALLY CYLINDRICAL CHAMBER, A WIRE COIL INSIDE AND CONCENTRIC WITH THE CHAMBER, MAGNETIC POLE PIECES SECURED TO THE HOUSING WITHIN THE CHAMBER, THE POLE PIECES PROJECTING TOWARD EACH OTHER WITHIN THE COIL WITH THEIR INNER ENDS SPACED APART TO FORM A NON-MAGNETIC GAP, AN OUTPUT SHAFT JOURNALLED IN THE HOUSING AND EXTENDING THROUGH THE CHAMBER WITHIN THE COIL, THE SHAFT BEING POSITIONED AWAY FROM THE AXIS OF THE COIL AND CHAMBER, AN ELONGATED 